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<div class="titlepage"><div><div><h3 class="title">
<a name="odtone.extensions.local_discovery"></a><a class="link" href="local_discovery.html" title="Local discovery">Local discovery</a>
</h3></div></div></div>
<p>
        Due to the decoupled architecture of the MIHF and the local entities (i.e.
        Link SAPs and MIH-Users), it is necessary to configure these entities in
        the MIHF in order to know about its existence. They can be configured statically,
        by the user, or automatically, using a discovery mechanism. The static configuration
        can be very limited, and may fail when, for example, the MN activates/deactivates
        an interface or even hot-plugs new ones. However, the IEEE 802.21 standard
        does not define any mechanism to discover the local entities so, the development
        of a novel local discovery procedure is required, allowing the MIHF to discover
        its Link SAPs and MIH-Users and their capabilities in a dynamic way. Thus,
        local discovery refers to the procedure that allows the MIHF to discover
        its Link SAPs and their capabilities, as well as its MIH-Users.
      </p>
<p>
        <span class="bold"><strong>Link SAP Discovery</strong></span>
      </p>
<p>
        <span class="inlinemediaobject"><img src="../.././images/Internal_link_discovery.png" alt="Internal_link_discovery"></span>
      </p>
<p>
        The local discovery mechanisms implemented on ODTONE enables the discovery
        and management of the available Link SAPs. Thus, Link SAPs discovery is divided
        in three main phases: the registration, SAP availability and SAP unavailability.
      </p>
<p>
        In the registration phase, the MIHF is permanently listening for incoming
        messages from the Link SAPs at a fixed port. When a Link SAP becomes active,
        it locally sends a "Link_Register.indication" message to the MIHF
        indicating its intention to register with the MIHF. This message carries
        information about the Link SAP, including its ID, listening port, link layer
        technology and link address. Next, the MIHF requests the Link SAP for its
        capabilities by sending a "Link_Capability_Discover.request" message.
        This process is repeated for all Link SAPs in order to provide the MIHF with
        the full capabilities belonging to that node.
      </p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top">
<p>
          Because there is no primitive/message in the 802.21 standard that allows
          the Link SAP to send the register information to the MIHF, the "Link_Register.indication"
          message was created. This message allows the Link SAP to send informations
          to the MIHF about which technology supports and which interface it manages.
          Associated with the creation of this new message type was also created
          a new TLV type named &#8220;Interface Type Addr TLV&#8221; whose correspondent
          data type is a &#8220;LINK_ID&#8221;.
        </p>
<p>
          <span class="inlinemediaobject"><img src="../.././images/link_register_indication_message.png" alt="link_register_indication_message"></span>
        </p>
</td></tr>
</table></div>
<p>
        The second phase is availability and, as the name implies, deals with the
        Link SAP availability, i.e., the MIHF must be able to detect the active presence
        of the Link SAP. So, when the MIHF receives a response or an event notification
        from the Link SAP, it detects the Link SAP as active.
      </p>
<p>
        Finally, the third phase deals with SAP unavailability. When the MIHF does
        not receive a response from a Link SAP, the Link SAP must be considered as
        inactive or unresponsive. The MIHF must, therefore, initiate the procedures
        to update its local capabilities.
      </p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
          The waiting time interval for response message and how many fail responses
          can occur before the MIHF forget Link SAP can be defined at the MIHF configuration
          file.
        </p></td></tr>
</table></div>
<p>
        <span class="bold"><strong>MIH User Discovery</strong></span>
      </p>
<p>
        <span class="inlinemediaobject"><img src="../.././images/Internal_user_discovery.png" alt="Internal_user_discovery"></span>
      </p>
<p>
        The process of discovering MIH-Users implemented on ODTONE is based on a
        registration process of the MIH-User with the MIHF. When the MIH-User becomes
        active, it locally sends a "User_Register.indication" message to
        the MIHF, including information about its listening port, supported commands
        and/or supported queries.
      </p>
<p>
        Upon the reception of the "User_Register.indication" message, the
        MIHF learns about the MIH-User and the communications between them can start
        normally.
      </p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top">
<p>
          Because there is no primitive/message in the 802.21 standard that allows
          MIH-User to send register information to the MIHF the &#8220;User_Register.indication&#8221;
          message was created. This message allows the MIH-Users to send informations
          to the MIHF about the supported commands and/or queries.
        </p>
<p>
          <span class="inlinemediaobject"><img src="../.././images/user_register_indication_message.png" alt="user_register_indication_message"></span>
        </p>
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      Aveiro<br>Copyright &#169; 2009-2012 Instituto
      de Telecomunica&#231;&#245;es - P&#243;lo Aveiro<p>
        This software is distributed under a license. The full license agreement
        can be found in the LICENSE in this distribution. This software may not be
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        agreement. This software is distributed without any warranty.
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